Unlike Alonso's Indy 500 experience this year, Senna only did some test driving at an Arizona proving grounds, but it still left an impression on those who were present for the test. He was testing with the Penske racing team, which had Emerson Fittipaldi and Paul Tracy as the primary drivers. And apparently it didn't take long for Senna to start matching and beating their times. Tracy is interviewed in the documentary, and he talks about how Senna's driving style was different and that Tracy paid close attention to learn how he could improve his own driving.
The various people featured in the documentary all talk about how Senna seemed to really enjoy driving the car as well. Tony Kanaan, who later drove IndyCar, says Senna told him how much fun it was and that Kanaan should look into the series. But apparently the test wasn't entirely just a curiosity in the sport, but also a strategy to get paid more in Formula One, which the documentary says was quite successful.
If you're a Senna fan, or just a motorsports fan in general, this documentary is well worth the 26 minutes to watch. It's an interesting, overlooked little side story in the history of one of F1's greatest drivers.